This invention relates to an exposure compensation apparatus for use in a radiographic equipment for medical diagnosis.
In conventional radiographic apparatus, a radiation source applies radiation, generally X-rays, to an object, generally a covered organ in a living human body, to form and record an image of the object on an image screen, such as an screen-film installed behind the object.
In X-ray diagnosis, however, the object, a chest for example, has extremely great variations in anatomical thickness and tissue hardness, thus causing a great deal of variance of X-ray absorption by portions of the object.
As a result, only a small part of the object image is provided with an appropriate exposure amount and a greater part of the image is out of the proper exposure range, and this causes a large loss of image information, namely a large loss in diagnosis value.
To meet the above situation a local intensity modulator is installed between the radiation source and the object, and is used for the purpose of modulating the intensity of the radiation to each location of the object, whereby the modulation is based on transmittance datum of each location measured by test radiation that is radiated before or at substantially the same time of said radiation, as referred to in the Japanese patent publication Nos. 1987-129034 and 1988-189853.